Digital micro-mirror devices (DMDs), are used for various applications, and most commonly as a spatial light modulator for imaging applications. The DMD has an array of thousands of tiny tilting mirrors. To permit the mirrors to tilt, each is attached to one or more hinges mounted on support posts, and spaced by means of an air gap over underlying control circuitry. The control circuitry provides electrostatic forces, which cause each mirror to selectively tilt. The mirror tilts in one direction (off) and in another direction (on), thereby modulating the light incident on its surface. Light reflected from on mirrors passes through imaging optics and to the image plane. Light from the off-mirrors is reflected away from the image plane.
U.S. patent Ser. No. 08/171,303, entitled "Improved Multi-level Digital Micromirror Device", provides a comprehensive description of a "hidden hinge" type DMD and its use in imaging applications. Other types of DMDs are described in the following patents: U.S. Pat. No. 4,566,935, entitled "Spatial Light Modulator and Method"; U.S. Pat. No. 4,615,595, entitled "Frame Addressed Spatial Light Modulator"; U.S. Pat. No. 4,662,746, entitled "Spatial Light Modulator and Method"; U.S. Pat. No. 5,061,049, entitled "Spatial Light Modulator and Method"; U.S. Pat. No. 5,083,857, entitled "Multi-Level Deformable Mirror Device"; and U.S. Pat. No. 5,096,279, entitled "Spatial Light Modulator and Method." These patents and patent applications are assigned to Texas Instruments Incorporated and are incorporated by reference herein.
As a result of manufacturing problems, it may happen that one or more mirror elements of a DMD do not tilt at the correct angle on or off. It is desirable to have some means of testing DMDs for such defects.